1. Field of the Invention
The present invention relates to a speaker, and more particularly, to a speaker including a substantially hemispherical vibrator.
2. Description of the Related Art
The structure of a conventional speaker will be explained with reference to FIGS. 4, 5 and 6 which speaker is described Japanese Unexamined Patent Publication No. 9-322283.
As seen in FIGS. 4-6, a speaker 1 includes a hemispherical vibrator 2. The vibrator 2 has a hemispherical vibrating body 4 made of a piezoelectric material such as ceramic. To vibrate the vibrating body 4, electrodes 6a and 6b are provided respectively on a curved inner surface and a curved outer surface of the vibrating body 4 so as to provide a driving member for driving and vibrating the vibrating body 4. The vibrating body 4 is polarized along its width.
Furthermore, the vibrator 2 is connected to a horn 8 made of synthetic resin. The horn 8 includes an upper base 10, a supporting member 16, a first cylinder 30, a second cylinder 32, a third cylinder 34, a fourth cylinder 38, a fifth cylinder 42 and a lower base 46.
The upper base 10 has a projection 12. A flange 14 is provided around the projection 12, and a hole 20 is provided inside the projection 12. Furthermore, a ring-shaped convex portion 22, which is triangular in cross-section, is arranged so as to surround the opening of the hole 20, a ring-shaped flat portion 24 is arranged so as to surround the convex portion 22, a ring-shaped convex portion 26 is arranged so as to surround the flat portion 24, and finally, a ring-shaped flat portion 28 is arranged on the outermost side so as to surround the convex portion 26. Furthermore, a ring-shaped groove 16a is provided in one main surface of the supporting member 16.
The ring-shaped rim 2a of the vibrator 2 clips into the groove 16a of the supporting member 16, the groove 16a is filled with urethane resin (not shown in the Figures) and when the urethane resin hardens, the vibrator 2 is thereby secured to the supporting member 16.
The vibrator 2 is attached around the outer rim of the projection 12 of the upper base 10, with the supporting member 16 disposed in between the vibrator and the projection 12. Thus, the vibrator 2 is arranged so as to cover the projection 12, and a cavity 18 is defined between the vibrator 2 and the projection 12 to allow the vibrator 2 to vibrate. The electrodes 6a and 6b of the vibrator 2 are connected via a conductive ribbon (not shown in the Figures) to an input terminal (not shown in the Figures), which is provided on the outer side of the vibrator 2.
Alternatively, the supporting member 16 may be formed as a single integral body with the upper base 10.
Furthermore, one end of the first cylinder 30 is inserted through the hole 20 in the upper base 10 to the head of the projection 12. The inner rim surface of one end of the second cylinder 32, which has a larger diameter than the first cylinder 30, attaches to the outer rim of the other end of the first cylinder 30, and in addition, the inner rim surface of one end of the third cylinder 34, which has a larger diameter than the second cylinder 32, is attached to the outer rim of the other end of the second cylinder 32. Multiple V-shaped notch portions 36 are provided at equal intervals roughly all the way away around the other end of the third cylinder 34.
The notch portions 36 gradually widen as they are located closer to the end surface of the other end of the third cylinder 34.
Furthermore, the end surface of one end of the fourth cylinder 38, which has a larger diameter than the third cylinder 34, is attached to the flat portion 24 of the upper base 10. Multiple V-shaped notch portions 40 are provided at equal intervals roughly all the way around the other end of the fourth cylinder 38. The notch portions 40 gradually widen as they are located closer to the end surface of the fourth cylinder 38.
Furthermore, the surface of one end of the fifth cylinder 42, which has a larger diameter than the fourth cylinder 38, is attached to the flat portion 28 of the upper base 10. Multiple V-shaped notch portions 44 are provided at equal intervals roughly all the way around the other end of the fifth cylinder 42. The notch portions 44 gradually widen as they are located closer to the end surface of the fifth cylinder 42.
Furthermore, the lower base 46 has a cone-like convex portion 48, a ring-shaped flat portion 50, a ring-shaped convex portion 52 and a ring-shaped flat portion 54. The end surfaces of the other ends of the third cylinder 34 and the fourth cylinder 38 are affixed respectively to the flat portions 50 and 54 of the lower base 46.
Furthermore, a sound path is provided inside of the vibrator 2 and the horn 8. The cross-sectional area of the sound path widens in steps from the inner surface of the vibrator 2, via the first cylinder 30, the second cylinder 32 and the third cylinder 34, and as indicated by the arrow P in FIG. 5, loops from the notch portions 36 of the third cylinder 34 via the fourth cylinder 38, reaching the fifth cylinder 42 via the notch portions 40, and arriving at the notch portions 44 of the fifth cylinder 42.
In the speaker 1 having such a construction, when an electrical signal is input to the input terminal, the vibrator 2 vibrates, whereby sound waves are emitted from its outer surface. In addition, sound waves are emitted from the inner surface of the vibrator 2 via the cavity 18 and the sound path. Since the vibrator 2 is hemispherical, nondirectional sound waves are transmitted in a direction parallel to the surface of the device and the floor surface or surface supporting the speaker 1.
Since the vibrator 2 is hemispherical, the sound waves emitted from the curved outer surface of the vibrator 2 are emitted in all directions relative to the surface supporting the speaker or the floor surface, and are consequently nondirectional. Furthermore, the sound waves which are emitted from the curved inner surface of the vibrator 2, via the cavity 18 and the sound path, are transmitted in all directions relative to the surface of the speaker and the floor surface, and are consequently nondirectional. In this way, the speaker 1 is nondirectional relative to the surface supporting the speaker, i.e. the floor surface.
Furthermore, in the speaker 1, the ring-shaped rim 2a of the vibrator 2 is secured by contacting the bottom 16a1 of the groove 16a of the supporting member 16, so that the vibrations of the vibrator 2 are damped, thereby obtaining desired impedance characteristics and ensuring even a sufficient sound pressure.
However, when the speaker 1 experiences extremely high temperature and moisture in environmental tests and the like, there are occasions in which the urethane resin, which fills the groove 16a of the supporting member 16, expands and the urethane resin rises up together with the vibrator 2, causing a cavity to be defined between the vibrator 2 and the bottom 16a1 of the groove 16a. When such a cavity occurs, there is a danger that the vibrations of the vibrator 2 cannot be adequately damped, the desired impedance characteristics cannot be obtained, and as a result, evenness of the sound waves is hindered.